Lbn cal values measured 06dec01
04mar0
(note: these cal values have not been installed on the system. The page
is for reference)
The cal values for lband narrow were measured
on 06dec01 in the morning using the sky/absorber
technique tracking blank sky. The cal on/off times were 5 seconds
. This data was taken with the radar blanker on for only the sky measurements.
After looking at the data it became obvious that we need to blank the radar
while we are also on the absorber. We cycled through the range 1200->1600
Mhz only twice. To do a better job at filtering we need to cycle through
the entire range many more times (see
data from 28jan02). Another problem with this data was that the routine
had a bug and repeated the frequency 1350->1375 twice and did not take
any data in 1375->1400 Mhz (this had been fixed).
The temperatures used in the computation were:
| Tsky+Tabsorber |
20 K |
| Tabsorber |
302 K |
| Treceiver |
16 K polA
12 K polB |
Each frequency band was measured 2 separate times on the absorber and
sky. For each measurement the calon/off-1 spectrum was computed and
then the 2 separate measurements were cumfiltered to remove rfi. The cal
Value versus frequency plots show the results.
-
Fig 1 is the cal value in deg K versus frequency. The * are the measurements
and the lines are the cumfiltered values at each frequency. The colors
are: Blue is measured using the sky and absorber ratio. Black is using
just the absorber and red is using just the sky. The Top plot is polA and
the bottom plot is polB. The purple line is the current cal value (with
the 6% error). The light blue line is the current cal value after correcting
for the 6% error. The cal value from the sky does not agree very well with
the values from the absorber and absorber, sky ratio.
-
Fig 2 and 3 show the cal values for each measurement (polA, polB). The
top plot has the 2 measurements on the absorber. The center plot shows
the 2 measurements on the sky. The bottom plot is the absorber, sky ratio.
The measurements on the absorber polA did not repeat the same values. The
sky measurements were repeatable above 1300 Mhz.
The spectra
of calOn/Caloff-1 for the 2 sky measurements has jumps
in the 1375->1400 Mhz spectra (which were actually repeats of 1350 to 1375).
Below 1300 and above 1500 Mhz there is a lot of rfi. The blanking does
a pretty good jump for the 1330,1350 radar's. It turns out that the absorber
spectrum also had radar interference in it. We should have run the blanker
for the absorber as well.
The final plot
has the power levels during the measurements.
-
Fig 1 top is the power at the upstairs fiber optic transmitter for all
of the measurements. Each green vertical line delimits a single pass through
1200 to 1600 Mhz (there were 2+2=4 in total). This averages over 500 Mhz
and is taken before the start of each 100 Mhz band.
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Fig 1 center is the power at the downstairs if power meter.
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Fig 2 plots the 50 Mhz band (via the power counters) that is input to the
correlator 8 bit a/d converter. Top to bottom is correlator board 1 (first
25 MHz of 100 MHz section) through board 4 (last 25 MHz of the 100 Mhz
section). The level has been divided by the median value (the scale is
linear in power). The jumps in board 1 are the 1325 to 1350 radars.
-
Fig 3 plots the 25 Mhz 9 level total power measured via the 0 lag of the
correlator. A 25 MHz digital filter sits between the power counter of figure
2 and this measurement.
This was the first attempt at taking data this way. What we learned was:
You need to blank the absorber as well as the sky.
You need to repeat the entire sweep through the 1200 to 1600 band many
times so you can do a better job of filtering the rfi out. This will also
help the absorber measurement to get a better average since Tsys is 300
degrees.
You should probably extend the integration time from 5 seconds to 10 or
12 seconds so that the radar rotation period of 10 or 12 seconds does not
preferentially fall in the cal on or the cal off and give a biased value.
The filtering methods work better if the excursions are equal in the positive
and negative directions from the median.
processing: x101/011206/lbninp.pro,lbncal.pro,lbnspec.pro,lbndiag.pro
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